My car is scenario #1. Bought 1 owner v6 Monte(exactly like my first car when I was 18 in 1998). Toss out v6, Brand new 350, transmission professionally rebuilt by the best, fully custom exhaust, few suspension and other upgrades, 15" rims, keep overall stock look. I have $13,000 invested including purchase price(and this was in 2011). The car runs and drives amazing. With a brand new engine and transmission it's nearly as reliable as my wifes 2015. This car means the world to me but what could I get if I sold it? $7,500 on my best day, If I came across that right guy just like me who had the same exact car as a teenager but would like to re-live those days but with a V8 and sweet exhaust. Otherwise the sale process would be a nightmare of lowballers assuming I'm getting divorced or some other life calamity forcing me to sell. They wouldn't even be interested in the car as much as they would be interested in beating me down and seeing me die inside a little.
Scenario #2 would be better financially but there are 2 problems.
Problem 1: You're sort of beholden to the original car. You get a Mint SS with T-tops for example and you really can't tinker with it. If you ruin the originality you ruin the cars value. So you're stuck with a 305 when a sweet engine swap is just to easy to execute in that car. For many that might be fine if your just boulevard cruising and you simply love the nostalgia of an all original 80's car.
Problem 2: Every time I'm on ebay or CL I see wildly varrying prices for Monte SS's. There are always many to choose from and you'll always see a low mile, great condition all original SS which is properly documented and (according to the owner) valued at 16k. Then some old timer who doesn't have time to maintain his anymore is basically giving away his 1 owner, dealer serviced and always garaged one which is a ball hair away from being as nice as the last one you saw but this one is 8 grand. Oh but it needs new weather stripping for the T-tops and a radio fuse(big deal right?). Point being many of these have been garaged and since they aren't 69 Chevelle's what it's worth is